Signal convolution involves the detection of one or more particular characteristics of a signal, or combination of signals, in such a way that a particular characteristic of interest is reinforced or supressed. Convolution is one mechanism for permitting received signals to be interpreted with regard to a known reference signal, such as may be useful with radar, sonar and other similar systems. Convolution requires the storage of two signals over the sampling time, point by point multiplication of the signals and integration of the associated products.
Surface acoustic wave technology has been used to practice convolution, although these prior devices have had a number of drawbacks relating to propagation of the signals along the substrate surface. Furthermore, the signals were launched through a common delay line, thereby permitting "self-convolution" to occur due to signal reflection from one transducer or the other. Self-convolution is not desirable because the resulting output signal depends on only one input signal, rather than being produced when both input signals are non-zero.
Surface acoustic wave signals in the prior devices were extracted from the original signal source, thereby reducing the available energy for signal transport. Signal strength degrades per unit length, so that the devices had a finite useable length, which length limited the length of the coded signal which could be interpreted. Cascading of devices was not possible because of the signal degeneration.
From the above, it can be seen that there is a need for a convolver which overcomes the drawbacks of the prior art surface acoustic wave convolution devices. The disclosed invention is just such a convolver and avoids "self-convolution" by utilizing separate delay line channels, permits longer channel lengths to be utilized because the signal transport energy is not diminished by sampling, and also permits cascading of convolvers to permit longer length coding sequences to be interpreted.